Disable some image_test cases with concurrent collector.

The following image_test cases sometimes fail on ART Builbot's
x86 concurrent collector configuration:
- ImageTest.WriteReadUncompressed
- ImageTest.WriteReadLZ4
- ImageTest.WriteReadLZ4HC
Disable them to make the build turn green again, while we
investigate the failures.

Bug: 27578460
Change-Id: I46126e4690e6300e3bfa771c1b6a560272ecb1da
diff --git a/compiler/image_test.cc b/compiler/image_test.cc
index 91579e9..7779e44 100644
--- a/compiler/image_test.cc
+++ b/compiler/image_test.cc
@@ -288,14 +288,17 @@
 }
 
 TEST_F(ImageTest, WriteReadUncompressed) {
+  TEST_DISABLED_FOR_READ_BARRIER();  // b/27578460
   TestWriteRead(ImageHeader::kStorageModeUncompressed);
 }
 
 TEST_F(ImageTest, WriteReadLZ4) {
+  TEST_DISABLED_FOR_READ_BARRIER();  // b/27578460
   TestWriteRead(ImageHeader::kStorageModeLZ4);
 }
 
 TEST_F(ImageTest, WriteReadLZ4HC) {
+  TEST_DISABLED_FOR_READ_BARRIER();  // b/27578460
   TestWriteRead(ImageHeader::kStorageModeLZ4HC);
 }